Preparation Of Polyurethane Based Composite Films And Their Applications In Flexible Driving,Energy Storage And Flexible Sensors

Since the 21st century,with the development of science and technology and the rise of living standards,the technology of flexible electronic devices has taken on a new look and has achieved great development in the fields of human health monitoring,flexible energy storage,wearable electronic devices,flexible sensing and so on.Traditional silicon based electronic devices（such as Huawei band,Google Glass,etc.）can no longer meet the needs of people.Therefore,it has important research significance to prepare flexible and high-performance flexible electronic equipment by simple and efficient technology.More importantly,although today’s flexible electronic equipment has achieved excellent performance,but they are still faced with many problems in practical application.For example,dielectric elastomer actuators based on polymer/ceramic packing systems may suffer from problems such as reduced breakdown strength and mechanical properties due to packing agglomeration.In addition,the flexible sensor has complex preparation process,low sensitivity and slow response.When performing human body monitoring and other work,external power supply is required to provide endurance problems.Therefore,it is of great significance to solve the above problems.Based on polyurethane（TPU）composite films,this study achieved the dielectric property,flexibility,ferroelectric energy storage,electric drive,piezoelectric property and other functions of the polyurethane composite films through simple and efficient solution pouring method and layer-by-layer electrostatic spinning.The applications of polyurethane composite films in dielectric elastomer drivers,energy storage,piezoelectric nanogenerators and strain sensors were realized.In the field of flexible electronics,the further development of materials,preparation process and application had been promoted.The main research contents and results were as follows:（1）In the polyurethane/Barium titanate（TPU/BaTiO₃）composite material system,the compatibility between the filler and the matrix could be improved by adjusting the doping ratio of the filler and the thermal treatment process to enhance the interface compatibility.The results showed that the dielectric constant of the composite film reached 7.3 at the test frequency of 1 k Hz after thermal treatment at 150℃.The elongation at break reached 1934%and the elastic modulus decreased to 4.4 MPa.In addition,under the electric field of 300 k V/cm,the discharge energy density reached 73 m J/cm³,and the charge-discharge energy conversion efficiency was as high as 84%.More importantly,the electric drive displacement of 2.61mm was 1.7 times that of the untreated composite at an electric field of 160 k V/cm.The system had a good application prospect in dielectric elastic actuator and flexible energy storage.（2）By electrospinning and layer-by-layer electrospinning,polyvinylidene-hexafluoropropylene（P（VDF-HFP））piezoelectric nanofibers doped with different concentrations of MXene and TPU nanofibers were used to construct MPFP/TPU multilayer composite fibers.The results showed that the sensitivity reached 0.38 k Pa^-1,the response/recovery time was 210 ms/100 ms,and the piezoelectric output stability was good.The output voltage reached 25 V under the action of palm pressing.The MPAN/TPU multilayer composite fibers were constructed by MXene doped polyacrylonitrile（PAN）piezoelectric nanofibers and TPU nanofibers.The results showed that the sensitivity of the four-layer 1MPAN/TPU/1MPAN/TPU composite fiber reached 0.16k Pa^-1,respectively.The response/recovery time was 150 ms/140 ms,and the output voltage was 30 V under the action of palm press.Piezoelectric nanogenerators based on multilayer composite fibers showed excellent potential in human energy harvesting and motion monitoring.（3）The TPU composite fiber system doped with MXene and ionic liquid（ILs）,and the dual-conductive network of MXene and ILs was constructed by doping the solution on the TPU nanofiber network.The results showed that the conductivity of the composite fiber increased obviously with the doping of the conductive filler.The conductivity of TPU,TPU-0.5MXene and TPU-0.5MXene@10ILs were 1.65×10^-10,5.5×10^-10and 2.03×10^-6 S/cm,respectively.In addition,the energy loss density increased significantly due to leakage current,and only 32%energy conversion efficiency and 18 m J/cm³ energy storage density under 260k V/cm electric field.In addition,TPU-0.5MXene@10ILs composite fibers had a sensitivity of 1.06,but also had good strain sensing stability.The TPU-MXene@ILs composite fibers provided a new strategy for the preparation of high performance strain sensors,which was expected to be applied to human motion detection,physiological monitoring and other fields.